MongoDB / Meteor: Multiply entire array within collection - arrays

Question

I have a problem with multiplying an array of key-value pairs in Meteor / MongoDB. I want to multiply an entire ingredient list with a fixed value. The collection looks like this:
"ingredients" : [
{
"ingredient" : "noodle",
"amount" : 500,
"unit" : "g"
},
{
"ingredient" : "cheese",
"amount" : 100,
"unit" : "g"
}
],
Now, I want to multiply the amount value with a certain number multip, let's say 1,5. The desired output would look like:
"ingredients" : [
{
"ingredient" : "noodle",
"amount" : 750,
"unit" : "g"
},
{
"ingredient" : "cheese",
"amount" : 150,
"unit" : "g"
}
],
Right now I have this:
for (i in this.ingredients){
var precalc = this.ingredients[i].amount * multip; //Here's the Multiplicator
var prez=this.ingredients[i].ingredient;
var prem=this.ingredients[i].unit;
Recipes.update(
{"_id": this._id},
{"$set": {
"ingredients":[{ingredient:prez, amount:precalc, unit:prem}]
}}
);
}
I precalculated the new value and used $set because apparently the $mul operator isn't working with meteor. This solution partly works, but unfortunately it overwrites all ingredients and only multiplies the last one (which is obvious). There must be a much simpler way to do that - I just didn't find it. I'm new to MongoDB and Meteor so any help is greatly appreciated!

Answer 1

Don't execute an update for each ingredient, only one for the entire document. I'd do something like this:
let newIngredients = this.ingredients.map(x => {
ingredient: x.ingredient,
amount: x.amount * 1.5,
unit: x.unit
});
Recipes.update(
{_id: this._id},
{$set: {ingredients: newIngredients}}
);